This invention relates to the creation and presentation of stereoscopic images.
The present invention derives from a stereoscopic drawing process sometimes referred to as a phantogram. This is a public domain drawing procedure, usually done in two-color anaglyphic process, and dates from approximately the beginning of the twentieth century. Objects are drawn resting upon a horizontal image, or ground, plane, and have stereoscopic parallax and linear perspective applied to them while the ground plane itself remains rectilinear. The resulting stereogram is then placed flat on a desk in front of the viewer. The image is viewed obliquely at some angle, commonly 45 degrees down. When the viewer attains the proper viewing angle and viewing distance, the objects in the stereogram appear orthostereoscopic, properly proportioned, and apparently occupying the same X-Y-Z coordinate space as the viewers environment. The effect is quite palpable, almost holographic, prompting the viewer to attempt to touch and interact with the virtual objects.
The phantogram can be constructed through rigorous geometric plotting or by the use of commercially available grids. Phantograms have been most successfully used to illustrate spatially complex mathematical and geometric principles. Until now, this unique and relatively obscure approach to stereoscopic imaging has been limited to monochromatic line drawing. It would be useful to apply this approach to full-color, continuous-tone photography and photo-realistic, three-dimensional (xe2x80x9c3Dxe2x80x9d) computer graphics.
Most stereoscopic imaging and viewing systems, including binocular stereoscopes, projection devices, anaglyphic printing and CRT display, present the viewer with a 3D scene which may or may not correspond with his X-Y-Z coordinate space, usually not. That is, the angle and direction of regard of the imaging mechanism, be it photography or graphics, to the subject do not match the angle and direction of regard of the viewer to the resulting stereoscopic image. Objects commonly do not appear geometrically correct; they may be stretched or compressed along the viewing axis. Nor do they always appear to be the correct size. Additionally, if the imaging device describes the scene from one angle, say looking down, and the viewer regards the resulting stereo image horizontally, there is a lack of kinesthetic agreement. The compounding of these disagreements diminishes the effectiveness of the stereoscopic illusion, particularly if it is photographic or photo-realistic.
Through careful preplanning it is possible to display a stereoscopic image which is orthostereoscopic. That is, the angle of regard of the taking lens, in photography, or the lens of the virtual camera, in photo-realistic 3D computer graphics, exactly matches the viewer""s angle of regard to the resultant stereoscopic image. Now all objects in the scene will appear geometrically correct. But even the more rigorous requirements of orthostereo do not guarantee that objects will appear correctly sized. Nor does orthostereo demand a correlation between the viewing direction of the taking mechanism to the subject and the viewing direction of the viewer to the stereoscopic image. Kinesthetic disagreement may still result.
When all parameters of the imaging process agree with all parameters of the viewing situation, the resultant stereoscopic image will appear geometrically correct, objects will appear correctly sized, and the imaging angle to the subject will be duplicated by the viewing angle to the resultant image. The X-Y-Z coordinate space of the image is now congruent with the X-Y-Z coordinate space of the viewer. This situation is sometimes referred to as tauto-orthostereo and yields the strongest possible stereoscopic illusion. It is also almost never accomplished in usual stereoscopic practice due to the extremely stringent demands on the imaging and viewing procedures.
The phantogram imposes strict geometric parameters on the imaging and viewing conditions as an integral part of its creation, and is therefore guaranteed by definition to meet almost all the necessary requirements to be tauto-orthostereoscopic. From this it obtains its ability to present a powerful stereoscopic illusion. It is, however, still flexible in the area of apparent object size. Objects may or may not appear at 1:1 scale. This is a matter for the practitioner to decide. If the subject is a house, for example, it would require an inordinately large image to describe the subject at 1:1 scale as the image must accommodate the subjects rectilinear ground plane at full size. For objects of more modest scale, a telephone, for example, the ground plane can easily be accommodated and the resulting phantogram will be truly tautoorthostereoscopic.
Unique and appealing as the traditional phantogram may be, it is still just a line drawing. It lacks color, shading, photo-realistic detail and a true sense of solid, three dimensional reality.
It is an object of the invention to provide a method of viewing a stereoscopic image which appears geometrically correct.
It is an object of the invention to provide a method of viewing a stereoscopic image where the objects in the image appear to be the correct size.
It is an object of the invention to provide a method of viewing a stereoscopic image where the X-Y-Z coordinate space of the image is congruent with the X-Y-X coordinate space of the viewer.
The objects of the invention are met by a process in which a selected plane in a digitized set of stereo images is processed to remove the several distortions imposed on the images by the taking lens. The processing involves: 1) removing convergence toward the horizon; 2) removing foreshortening; and 3) removing horizontal skew. In one embodiment, the resulting stereogram is presented such that the ground plane of one of the images is coincident with some horizontal plane in the viewer""s environment. When the stereogram is viewed front an angle and distance which recapitulates that used in creating the stereo pair of images, an illusion of congruent depth results.
FIG. 1 is a pair of stereo images, each of the pair of images having a ground plane with the linear perspective imposed on the ground plane by the geometry of the taking lens.
FIG. 2 is the pair of stereo images shown in FIG. 1 after the convergence transform has been applied to remove convergence and perspective in accordance with the invention.
FIG. 3 is the pair of stereo images shown in FIG. 2 after the parallax transform has been applied to remove horizontal skew in accordance with the invention.
FIG. 4 is the pair of stereo images shown in FIG. 3 after the foreshortening transform has been applied to remove foreshortening in accordance with the invention.
FIG. 5 is the pair of stereo images shown in FIG. 4 wherein the ground plane of the left and right eye images are presented with their ground planes perfectly coincident.
FIG. 6 shows a common situation for viewing a photo-phantogram where the viewer is seated at a desk with the photo-phantogram resting on top of the desk.
FIG. 7 shows one possible embodiment for viewing large images in accordance with the invention.
FIG. 8 shows another possible embodiment for viewing very large images in accordance with the invention.